When diode high - speed conduction cut-off, parasitic parameters should be considered. During diode reverse recovery, the equivalent inductance and the equivalent capacitance become a RC oscillator, producing high frequency oscillations. In order to suppress this high frequency oscillation, a parallel capacitance C or RC buffer network is required at both ends of the diode. Resistance generally take 10 Ω Ω - 100, capacitance in 4.7-2.2 pf nf.
The value of capacitance C or RC in parallel on the diode is determined by trial and error. If you do not choose properly, it will cause more serious oscillation.
Diode back inductance (EMI filtering)
This is also a common method to suppress high frequency noise. According to the frequency of noise, choosing the appropriate inductor can also suppress the noise effectively. It should be noted that the rated current of the inductor should meet the actual requirements.
summary
These are some common ways to reduce output ripple in LED design, which may not be complete, but are sufficient for general applications. As for noise suppression, it is not always applied in practice. What is important is to choose the appropriate method according to your own design requirements, such as product volume, cost, development cycle and so on.

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